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mm/z3fold: fix z3fold_reclaim_page races with z3fold_free

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Think about the below scenario:

CPU1				CPU2
z3fold_reclaim_page		z3fold_free
 spin_lock(&pool->lock)		 get_z3fold_header -- hold page_lock
 kref_get_unless_zero
				 kref_put--zhdr->refcount can be 1 now
 !z3fold_page_trylock
  kref_put -- zhdr->refcount is 0 now
   release_z3fold_page
    WARN_ON(!list_empty(&zhdr->buddy)); -- we're on buddy now!
    spin_lock(&pool->lock); -- deadlock here!

z3fold_reclaim_page might race with z3fold_free and will lead to pool lock
deadlock and zhdr buddy non-empty warning.  To fix this, defer getting the
refcount until page_lock is held just like what __z3fold_alloc does.  Note
this has the side effect that we won't break the reclaim if we meet a soon
to be released z3fold page now.

Link: https://lkml.kernel.org/r/20220429064051.61552-9-linmiaohe@huawei.com
Fixes: dcf5aedb24 ("z3fold: stricter locking and more careful reclaim")
Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
Reviewed-by: Vitaly Wool <vitaly.wool@konsulko.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Miaohe Lin 2022-04-29 14:40:43 +08:00 committed by akpm
parent 4a1c383910
commit 04094226d6
1 changed files with 3 additions and 15 deletions
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18
mm/z3fold.c
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@ -519,13 +519,6 @@ static void __release_z3fold_page(struct z3fold_header *zhdr, bool locked)
atomic64_dec(&pool->pages_nr);
}
static void release_z3fold_page(struct kref *ref)
{
struct z3fold_header *zhdr = container_of(ref, struct z3fold_header,
refcount);
__release_z3fold_page(zhdr, false);
}
static void release_z3fold_page_locked(struct kref *ref)
{
struct z3fold_header *zhdr = container_of(ref, struct z3fold_header,
@ -1317,12 +1310,7 @@ static int z3fold_reclaim_page(struct z3fold_pool *pool, unsigned int retries)
break;
}
if (kref_get_unless_zero(&zhdr->refcount) == 0) {
zhdr = NULL;
break;
}
if (!z3fold_page_trylock(zhdr)) {
kref_put(&zhdr->refcount, release_z3fold_page);
zhdr = NULL;
continue; /* can't evict at this point */
}
@ -1333,14 +1321,14 @@ static int z3fold_reclaim_page(struct z3fold_pool *pool, unsigned int retries)
*/
if (zhdr->foreign_handles ||
test_and_set_bit(PAGE_CLAIMED, &page->private)) {
if (!kref_put(&zhdr->refcount,
release_z3fold_page_locked))
z3fold_page_unlock(zhdr);
z3fold_page_unlock(zhdr);
zhdr = NULL;
continue; /* can't evict such page */
}
list_del_init(&zhdr->buddy);
zhdr->cpu = -1;
/* See comment in __z3fold_alloc. */
kref_get(&zhdr->refcount);
break;
}